The
XSetOCValues function returns NULL if no error occurred; otherwise,
it returns the name of the first argument that could not be set. An argument
might not be set for any of the following reasons:

The argument is read-only.

The argument name is not recognized.

An implementation-dependent error occurs.

Each value to be set must be an appropriate datum, matching the data type
imposed by the semantics of the argument.

The XGetOCValues function returns
NULL if no error occurred; otherwise, it returns the name of the first
argument that could not be obtained. An argument might not be obtained for
any of the following reasons:

The argument name is not recognized.

An implementation-dependent
error occurs.

Each argument value following a name must point to a location
where the value is to be stored.

The XOMOfOC function returns the output
method associated with the specified output context.